Many coffee brewers and systems have been designed to brew coffee in small and large quantities. These systems range from small home-style brewers to large commercial brewers found in restaurants. Likewise, a large variety of coffee is available on the market from raw coffee beans of varying types to freeze-dried and other instant blends.
It is generally accepted that the best, most flavorful and desirable coffee is fresh batch-brewed coffee as is served in coffee houses and restaurants. Single-cup brewers such as found in some vending machines produce a coffee that is considered far less desirable.
There are many fresh batch-brewer systems which include a holding tank in which the brewed coffee is stored, mainly at the proper drinking temperature, and then dispensed on demand. This type of brewer, common in coin-operated machines, is also used in office coffee service and related systems. The quality of coffee from the hot coffee holding reservoir is good right after brewing, but continually decreases overtime until it becomes very strong and unpleasent tasting, which only takes about an hour.
The continual degrading in quality is primarily attributable to the need to keep the brew at an elevated temperature (approximately 170.degree. F.) in order to dispense the coffee at drinking temperature. The temperature is ordinarily maintained by added heaters or by designing a holding tank so that it holds a temperature over the required period because of its insulation. In any event, while the coffee is being held in this reservoir the elevated temperature causes an undesirable cooking of the coffee resulting in the evolution of an unpleasant taste.
Taste tests have shown that if the coffee is cooled after brewing to an ambient temperature, and then stored in the holding reservoir, and not heated until needed, the storage life is significantly increased. The strong, harsh taste is not present even after hours of storage. The only apparent degradation of flavor and aroma takes place only gradually, and even then does not start until more than three hours after the coffee has been brewed.